The present invention generally relates to radio frequency identification (RFID) and, more particularly, to an antenna configured for an RFID tag.
Radio frequency identification (RFID) is an important technology in the identification industry and has various applications. RFID tags or labels are widely used to associate an object with an identification code. For example, RFID tags have been used for access control to buildings, security-locks in vehicles and tracking inventory. Information stored on an RFID tag may identify a person seeking access to a secured building or an inventory item having a unique identification number. RFID tags can retain and transmit enough information to uniquely identify individuals, packages, inventory and the like. Generally, in an RFID system, in order to retrieve the information from an RFID tag, an RFID reader may send an excitation signal to the RFID tag using radio frequency (RF) backscatter technology. The excitation signal energizes the tag, which in turn backscatters the stored information to the reader. The reader then receives and decodes the information from the RFID tag.
An RFID tag may generally include a chip for data processing and an antenna for data communication. In the RFID industry, it may be important for an RFID tag to efficiently receive or use the energy received from an RFID reader so as to facilitate a subsequent response to the reader or increase an available radio range over which the tag can communicate with the reader in a wireless manner. The efficiency may be improved by impedance matching between the chip and antenna of an RFID tag. Since the chip generally exhibits relatively high capacitive impedance, the antenna may be designed with relatively high inductive impedance to achieve conjugate match. Such high inductive impedance, however, may adversely narrow down the bandwidth of the RFID tag. Furthermore, the material of a substrate that carries an RFID tag may cause variation in the desired inductive impedance of the tag. Also, the capacitive impedance of the chip may vary due to semiconductor manufacturing processes. It may therefore be desirable to have an RFID tag antenna that is able to form complex conjugation with a corresponding chip. It may also be desirable to increase the bandwidth of an RFID tag while achieving complex conjugation for impedance match between the tag antenna and the chip.